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Complements, Substitutes, and Giving Thanks

Thanksgiving is my favorite holiday. There is zero pressure to frantically search for presents, and it is an excellent opportunity to cook, bake, and eat. Thanksgiving is also a prime opportunity to think about economics. So what could be better?

Economics will definitely be on people’s minds this year (2021) as people think through what to purchase for the big meal. Food prices are on the rise and it is hard not to turn on the radio or read the news without a warning of potential food shortages in the weeks and days leading up to one of my favorite days. The food you buy for Thanksgiving is not exempt. The American Farm Bureau estimates prices for the Thanksgiving meal will be up 14%.

I’ve written about these food prices a couple times now (see this post on bacon and Biden's plan to combat meat price increases and this post on Russian export taxes and sunflower oil). As a reminder many things are driving it. There are shipping issues (fewer truck drivers domestically and port backlogs for international purchases), natural disasters (freezes, fires, droughts, floods, etc.), and labor shortages (not just of truck drivers). These supply issues are coupled with high demand as people return to restaurants, have extra cash on hand, and are gearing up for the food fest that is Thanksgiving.

Econ 101: decreasing supply + increasing demand = higher prices.

Now what does that have to do with complements and substitutes? Complements are things you consume together (think turkey and gravy). As the price goes up for one, the demand for the other will go down. The price of turkey is estimated to be up 24% per pound. One reason? The price of the food to feed the turkeys is higher! Therefore, if you are buying less turkey because the prices are higher, then you’ll need less gravy.

Maybe you even decide not to have turkey because of high prices and order a ham instead (a substitute). Substitutes are things you can — well — substitute between. With rising food prices, you might buy more ham (substitute) and less gravy (complement).

Prices of one good can increase or lower the demand of another good depending on whether the goods are complements or substitutes.

After the meal, you also have your desserts. At this point on a normal day there is probably no way you would have another bite of food. You are already full from all of that turkey, stuffing, mashed potatoes, green beans, peas, biscuits, and (of course) cranberry sauce. BUT, it is Thanksgiving and your dessert stomach (we all have one) is ready. You might be looking at a few different options of pie for dessert. Maybe it is pumpkin pie, pecan pie, cherry pie, apple pie, or a creamy and delicious chocolate pie. My family also throws in a couple other options for dessert. There is the unusual, but oh-so delicious, ambrosia (equal parts coconut, canned pineapple, canned oranges, marshmallows, and sour cream) and sweet potato casserole.

So what does this have to do with this year’s supply and price issues? The American Farm Bureau reports that the price of pumpkin pie filling is up 7% and the price of pre-made pie crusts is up 20%! Meanwhile, the price of sweet potatoes is only up 4%.

With the increase in price of pie crusts by 20%, you might decide to buy less pie filling because you won't make pie at all (filling and crust are COMPLEMENTS). Instead, you will then make sweet potato casserole (recipe below). Yes, the price of sweet potatoes have increased, but the price relative to the price of making a pumpkin pie has fallen, so you SUBSTITUTE sweet potato casserole for pumpkin pie.

So, as you buy your Thanksgiving meal, notice how you respond to the changes in prices. Are you buying more or less? Are they complements or substitutes?

Sweet Potato Casserole

Sweet potato casserole used to be a part of the main meal in our house. This caused competition on the plate with the mashed potatoes. Then one year I was making both a sweet potato casserole and a sweet potato pie for the same meal. I realized as I was putting them together that they basically contained the same ingredients except the casserole had marshmallows and the pie had flour. From that year on, we pulled the sweet potato casserole from the main menu and put it on the dessert menu. It had the added benefit of adding some room to our plates and allowing us to enjoy our meal a little bit more.

I have no idea where this recipe came from, but I’ve been making it for years and years and it is hard (impossible?) to mess up. I don’t measure out the sweet potatoes, but just guess. This year I used 4 decent sized sweet potatoes.



3 cups mashed, cooked sweet potatoes** (approximately 4 sweet potatoes)

1 cup sugar

2 eggs, slightly beaten

1 tsp. vanilla

½ cup milk

½ cup (1 stick) butter, melted and slightly cooled


1 cup brown sugar

1/3 cup flour

1/3 cup butter, melted and slightly cooled.

1-2 cups marshmallows, reserved.

Preheat oven to 350° for 30 minutes.

Combine ingredients for the base and put into a greased 9x13 pan.

Mix together the topping ingredients (just the brown sugar, flour, and butter) until crumble. Sprinkle on top of the sweet potato base.

Bake at 350° for 30 minutes**

After 30 minutes, take out the pan and sprinkle on marshmallows to cover the dish. Put back into the oven to 5-7 minutes, until marshmallows puff up a bit and are golden brown.

Serve warm!

*Warning* Potatoes always take longer to cook than you realize, so don’t leave this until the last minute. It usually takes about an hour for the sweet potatoes to be ready (I boil water and put slices of sweet potatoes in the water. I know they are done when a fork easily goes through them and the skins start to come off.) I actually boiled my sweet potatoes the week before I made this particular batch and then froze the potatoes before defrosting the day I put the casserole together. It is a nice way to save time when you are making a ton of things.

** A bonus is that you can put both the sweet potato casserole and your green bean casserole in the oven at the same time. You can then add the marshmallows and crispy onions when it is done and cook for five more minutes.


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